Tramadol has the chemical name (+/-)-trans (RR,SS)-2-[(di-methylamino)methyl]-1-(3-methoxyphenyl) cyclohexanol, and which is generally, and erroneously, referred to in literature as the cis(RS,SR) diastereomer, is a centrally acting, binary analgesic that is neither opiate-derived, nor is a non-steroidal, anti-inflammatory drug (NSAID). It is used to control moderate pain in chronic pain settings, such as osteoarthritis and postoperative cases, and acute pain, such as dental pain.
Used in therapy as a racemic mixture, the (+)-enantiomer binds to the .mu.-opioid receptor, and both enantiomers inhibit 5-hydroxytryptamine (serotonin) and noradrenaline (norepinephrine) reuptake. Tramadol's major active metabolite, O-desmethyltramadol (M1), shows higher affinity for the .mu.-opioid receptor and has at least twice the analgesic potency of the parent drug.
Despite the fact that tramadol is chemically unrelated to the opioids adverse side-effects associated with administration of tramadol are similar to those of the opioids.
The efficacy and safety of racemic tramadol and its separate enantiomers have been the subject of much study. It has been observed that the (+)-enantiomer has significantly higher analgesic potency than the (-)-enantiomer. It has also been observed that side-effects such as nausea and vomiting are more frequently experienced on administration of the (+)-enantiomer than the (-)-enantiomer. However, the conclusion drawn from these observations, taking into account efficacy and safety, has been to continue use of the racemate; see Pain 1995 September; 62(3):313--20 and Anaesthetist 1998 May; 47(5):387-94.